1. Field of the Invention
Apparatuses consistent with the present invention relate to an ultrasonic motor, and more particularly, to an ultrasonic motor with a vibrating element having a reduced weight while maintaining a required performance.
2. Description of the Related Art
Generally, an ultrasonic motor, for example, a traveling wave type hollowed ultrasonic motor, includes a vibrating element which generates a vibration, and a contacting element which rotates according to the vibration of the vibrating element. To generate the vibration, the vibrating element is provided with a piezoelectric body, which generates deformations or displacements due to a piezoelectric effect when it is applied with a voltage having a high frequency of more than 20 kHz.
Such an ultrasonic motor can be driven without separate reduction gears because it is driven at a low speed and a low torque unlike an electromagnetic motor driven at a high speed and a high torque. Further, the ultrasonic motor has a self-breaking function by using a friction force, enables a precise position control, and is compact, so that it can be applied to various system or devices. Accordingly, the ultrasonic motor is widely used in apparatuses, such as robots, medical treatment machinery and tools, optical devices, semiconductor inspection equipments, building automation systems, etc., which require an ultra-precision position control.
However, to allow the ultrasonic motor to have the required performance, it is necessary for the vibrating element to sufficiently transmit the vibration by the deformations of the piezoelectric body to the contacting element and thus to generate sufficient displacements on a contacting surface with the contacting element, and to have a proper coefficient of friction and a proper abrasion resistance on the contacting surface with the contacting element.
To meet such a condition, the vibrating element is usually formed of a material having a sufficient hardness and a sufficient abrasion resistance, for example, a bronze material, or a steel material, such as a quenched steel, a tool steel, a stainless steel, etc. However, because the materials as described above have a low machinability, they increase a machining cost in forming of the vibrating element, and thus a fabrication cost of the ultrasonic motor is increased. Also, because the materials are heavy, they impose restrictions on the range of systems or devices to which the ultrasonic motor can be used.